1. Field of the Invention
This invention relates to the separation of shredded plastic from processed shredded paper waste and more particularly to the use of electrostatic charging apparatus for such separation.
For conservation of natural resources, it is desirable to recycle paper derived from processed shredded waste. For this purpose the heavy materials commonly found in muniipal waste and including metal, glass, heavy plastics and the like are separated from the lighter fractions generally by air separation or classification. The separated shredded paper waste is useful as stock for papermaking. However, light plastic such as film plastic is a serious contaminant, causing plugging and fouling of the papermaking mahinery and resulting in imperfections in the final paper sheet. The use of film plastics is constantly increasing, so that the contamination of salvaged shredded waste paper is an increasingly serious problem where it is desired to recycle the processed shredded waste paper for papermaking. municipal
2. Description of the Prior Art
The general concept of separating sheet plastic film from paper and other waste is disclosed in U.S. Pat. Nos. 3,643,797 and 3,831,748. In these patents plastic film is caused to adhere to brushes by electrostatic attraction. A comb with teeth then removes the plastic film from the brushes. In these patents, the electrostatic brushes are horizontally mounted.
U.S. Pat. No. 3,458,040 discloses the electrostatic separation of material by means of alternate longitudinal strips of conducting and non-conducting material.
U.S. Pat. Nos. 2,428,224 and 3,941,684 also discuss electrostatic separation concepts less pertinent to the present invention.
Although the general idea of separating plastic waste materials utilizing electrostatic charge is known in the art, none of the systems or methods suggested provide adequate operating efficiencies for practical large volume, low cost installations. Among the problems typically encountered are the inadequacy of prior art systems in attracting all of the shredded light plastic such as film. The prior art systems do not retain the shredded light plastic to the attracting means in a stable manner so that light shredded plastic is not removed during the separation process. Finally, the prior art systems cannot efficiently handle a large volume of shredded waste over short periods of time.